1. Field of the Invention
This invention relates to a speed reducer for decelerating the rotation of the rotary shaft of a motor and obtaining a desired speed.
2. An apparatus of the construction shown in FIG. 1 of the accompanying drawings is known as a speed reducer. The construction of FIG. 1 is such that a first spur gear 2 having a toothed portion 2A is fixed to the shaft 1 of a motor, a second spur gear 6 supported by a case 4 and having a toothed portion 6A is in meshing engagement with the first spur gear and an output shaft 8 is fixed to the second spur gear. In the case of the above-described construction according to the prior art, the axis O.sub.1 of the shaft of the motor and the axis O.sub.2 of the reduction output shaft are not coincident with each other, but have an amount of deviation therebetween and therefore, it has been difficult to transmit the revolution of the motor to the output shaft 8 without causing eccentricity and run-out. Further, in the above-described construction, the outer diameters of the spur gears which perform the speed reducing action are great and it has been difficult to incorporate such apparatus into instruments which are required to be compact.
That is, in the conventional apparatus of FIG. 1, the distance between the shaft 1 of the motor and the axis of the output shaft 8 is determined by the mounted position of a motor case (not shown) and the speed reducing case 4 and the mounted position of the unshown bearing of the output shaft 8, and adjustment of these mounted positions is accomplished as by adjustment of mounting holes and mounting screws, and attainment of accurate mounted positions has been difficult. Furthermore, because of the tolerance of the finish dimensions of parts, there has been more or less irregularity in the individual speed reducers. Therefore, when the revolution of the motor is to be transmittted to the drive shaft of an FA (factory automation) instrument, not shown, through the speed reducer, it has been difficult for the revolution of the motor to be smoothly transmitted to the drive shaft, and this has also seriously affected the performance of the FA instrument.
Further, in the conventional speed reducer, where reduction gears are constructed in multistage to increase the reduction gear ratio, fastening means such as screws or caulking has been resorted to for the arrangement and coupling of the speed reducing units, and this has led to errors in the assembled position, which in turn has resulted in the lack of smoothness of the rotation transmitting portion. Also, if the number of stages of engagement between gears is increased to increase the reduction gear ratio, there are produced great sounds by the meshing engagement and rotation of the gears and thus, the conventional speed reducer has suffered from an undesirable problem as a speed reducer to be incorporated into a business machine.